Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • 2024-04

    • br Results br Discussion These results are in line with

    2018-11-06


    Results
    Discussion These results are in line with the known strong immunosuppressive effects of extracellular adenosine accumulation, mediated mainly through ADORA2A adenosine receptors (Sitkovsky and Ohta, 2005), and with previous reports showing the role of adenosine production by Tregs in immune response suppression (Deaglio et al., 2007; Kobie et al., 2006; Mandapathil et al., 2010; Schmitt et al., 2009). Moreover the cellular expression of ADORA2A in T melanotropin cost is directly proportional to the intensity of T cell response to adenosine (Apasov et al., 2000; Armstrong et al., 2001), inhibiting T cell activation and expansion (Huang et al., 1997). Concordantly, our results show that in co-culture, the presence of MSCs induced a higher expression of ADORA2A on CD4+ T cells. Also, adenosine concentration and CD39 expression were significantly higher on MSCs cultured with activated T cells. Adenosine levels in co-cultures (mean of 72ng/mL) are partially resultant from the production mediated by Tregs, nevertheless, at least more than half of the adenosine found in co-cultures can be attributed to MSCs, as adenosine concentration in the medium of MSCs cultured alone reached up to 43ng/mL. Moreover, when the medium of MSCs cultured alone was substituted by that of activated lymphocytes cultured alone (in the 3rd day of culture), the concentration rose up to 91ng/mL. Although it can be speculated that 5′-AMP generated from ATP by CD39+ Tregs could serve as substrate for the production of adenosine by CD73+ MSCs, our results indicate that MSC plays a major role in the production of adenosine in co-cultures. Our study also shows that MSCs induce lower expressions of ADA on CD4+ T cells. Although not statistically significant, ADA activity was higher in MSC co-cultures. It is possible that a larger number of samples would reveal a significant difference in ADA activity between cultures. The increased ADA activity observed may be explained, at least in part, by the lower percentage of CD4+ T cells expressing CD26, when in the presence of MSCs. With lower levels of CD26 more ADA molecules would be expected to be found free in the supernatant. Interestingly, even with higher ADA activity, adenosine levels were higher in co-culture. Mandapathil et al.(2010) revealed that low CD26 expression is a characteristic of naturally-occurring Tregs, whereas CD4+ T cells have elevated expression of this protein. Differently, we found that the expression of CD26 was higher in Tregs than in CD4+ T cells, in both culture systems. This elevated CD26 expression in Tregs may constitute a protective mechanism that increases ADA surface levels, preventing Tregs to be affected by adenosine signaling (Dong et al., 1996). Inversely, in CD4+ T cells co-cultured with MSC, the reduced expression of CD26, and the consequent low levels of ADA on the cell surface, would allow adenosine mediated suppression to occur. Recent data have shown that CD39 surface molecule is expressed predominantly in CD4+CD25hi Tregs (Mandapathil et al., 2010; Schmitt et al., 2009), suggesting that this ecto-enzyme may be useful to define human Tregs subsets (Borsellino et al., 2007; Dwyer et al., 2007; Schmitt et al., 2009). Differently than CD4+CD25hi Tregs, this CD4+CD25hiCD39+ subset is able to suppress pathogenic Th17 cells (Fletcher et al., 2009). Consistent with other authors, in our study, the CD39 was predominantly expressed in CD4+CD25hi Tregs, both generated in the absence or in the presence of MSC. CD73 can be detected in different cell types and it is possible that its physiological role differs according to the cell context (Zimmermann, 1992). Besides the enzymatic activity of CD73, its different functions include signal activation in leukocytes (Robinson, 1991) and T cell adhesion into endothelium (Airas et al., 1993). Recent data show that the expression of CD73 is very low in T cells, and that this protein is mainly localized in the cytosol of human naturally-occurring Tregs (Alam et al., 2009). Differently, murines present elevated CD73 expression on the surface of CD4+ T cells and CD4+CD25hi Tregs (Alam et al., 2009; Kobie et al., 2006). In our study, CD4+ T cells and CD4+CD25hi Tregs generated by T cell activation presented low CD73 expression on the surface and in the cell cytoplasm (data not shown). However, CD4+ T cells and CD4+CD25hi Tregs induced by MSCs showed increased levels of CD73 expression on the cell surface. These apparently conflicting results may be explained by methodological differences used in each study and the fact that CD73 stability on human cells surface is low (Thomson et al., 1990; Airas et al., 1993).